1. Field of the Invention
This invention relates generally to apparatus and methods for acquiring marine seismic data acquisition, and more particularly to marine seismic streamer positioning apparatus and methods of making and using same.
2. Related Art
Marine seismic exploration investigates and maps the structure and character of subsurface geological formations underlying a body of water. For large survey areas, seismic vessels tow one or more seismic sources and multiple seismic streamer cables through the water. The streamers may be positioned using controllable steerable birds, deflectors, steerable buoys, and the like.
Despite their wide use, some steerable birds may suffer from instability. Steerable birds comprising a body eccentric to the streamer with control surfaces attached to the eccentric body, unless very accurately ballasted to be perfectly neutrally buoyant, may tend to heel (list to one side) during use. This heeling will cause instability in the sense that a desired side force will always result in a vertical force component as well. Another factor of instability is the fact that the wings are attached to a body eccentric to the streamer and in such a way that the center of the lift force is eccentric from the streamer axis. This may result in the bird having different stability properties depending on the bird pulling (wing lift force acting away from the streamer) or pushing (wing lift force acting towards the streamer) on the streamer.
It would be an advance in the art if the stability of steerable birds comprising an eccentric body could be improved.